This invention relates to an apparatus for controlling the energy conversion process of an internal combustion engine and, more particularly, to such an apparatus utilizing a digital computer to process input sensor data and provide control signals to actuators in accordance therewith.
Electronic engine control systems are known that utilize a digital computer to receive input data indicative of engine operating parameters, calculate values corresponding to optimum settings of controlled variables such as fuel-injection timing, ignition timing, EGR-valve position, and the like, and provide control signals indicative of the calculated values to actuator means used to control the energy conversion process of an internal combustion engine. For such engine control systems, optimum settings for the controlled variables are different, for example, when the engine is idling than when the engine is operating normally.
In order to adjust a coefficient used in calculating a setting of the fuel control valve for controlling the quantity of fuel metered to the engine in the idle mode of operation, it is the conventional practice to employ a potentiometer electrically connected in a voltage divider circuit for supplying a voltage, the magnitude of which can be varied by rotating the potentiometer wiper shaft using a screwdriver. The voltage is applied to an A/D converter which converts it into a corresponding digital signal for application to the digital computer.
However, such coefficient adjustment employing one or more potentiometers having a potentiometer wiper mounted for sliding movement on a potentiometer resistor has several serious disadvantages. During vehicle operation, mechanical vibrations are transmitted to the potentiometers and cause defective contact between the potentiometer wiper and resistor, resulting in incorrect or unstable coefficient adjustment. Another disadvantage is that an attempt to increase the number of the coefficients to be handled requires an increased number of potentiometers, resulting in an expensive coefficient adjusting device. Furthermore, the number of the coefficients to be handled is limited due to the limitation on the number of the conversion channels of the A/D converter.
Therefore, the present invention provides a microprocessor-based electronic engine control apparatus employing an improved data adjusting device which is free from the above described disadvantages found in conventional devices.